st:why -recode-takes longer than -replace-

Dear Statalisters,
I am just curious about a fact noticeable when I use -recode- (1 as
following) or -replace- (2 as following) to recode all the variables
in a data set (size : 52,996,616) using Stata 10.1 SE: the recode
command takes much longer than replace. I was wondering what causes
the speed difference and if the speed difference implies for large
data set it would be better to use replace instead of recode.
1. slower
.recode _all (8=.) (9=.)
2. faster
foreach v of varlist * {
.replace `v'=. if `v'==8 | `v'==9
}
end
Thanks for your time!
Sincerely,
Amanda
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